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Abstract

We investigate the dynamical response of a quantum dot photonic integrated circuit formed with a combination of eleven passive and active gain cells operating when these cells are appropriately biased as a multi-section quantum dot passively mode-locked laser. When the absorber section is judiciously positioned in the laser cavity then fundamental frequency and harmonic mode-locking at repetition rates from 7.2GHz to 51GHz are recorded. These carefully engineered multi-section configurations that include a passive wave-guide section significantly lower the pulse width up to 34% from 9.7 to 6.4 picoseconds, as well increase by 49% the peak pulsed power from 150 to 224 mW, in comparison to conventional two-section configurations that are formed on the identical device under the same average power. In addition an ultra broad operation range with pulse width below ten picoseconds is obtained with the 3rd-harmonic mode-locking configuration. A record peak power of 234 mW for quantum dot mode-locked lasers operating over 40 GHz is reported for the first time.

Figures (6)

The layouts and probing scheme of the reconfigurable MLLs designed all within the same multi-section device. The probes biased with reverse voltage, gain currents and transparency current are colored in blue, red and cyan respectively. (a) A0.5G5.0, (b) A0.5P0.5G4.5. (c) A0.5P1.0G4.0. (d) A0.5G4.0P1.0. (e) A0.5G3.0G2.0. The light red indicts a lower current density. (f) G2.0A0.5G3.0, the asymmetrical configuration for higher order harmonic excitation (7th harmonic in this example).

(a). The measured net modal gain under CW pump and absorption spectra of the quantum dot active region. (b) The net modal gain at the wavelength of 1216nm from (a). The transparency current density is 1.5mA/section as shown with the arrow. The steady-state gain g0 of the configuration A0.5G5.0 is 4.2 cm-1 and the corresponding dg/dJ is 5.1×10-3 cm/A (point A). The g0 of the configuration A0.5P0.5G4.5 is 5.2cm-1 and the corresponding dg/dJ is 2.7×10-3 cm/A (point B). With a 1-mm passive waveguide section, the A0.5P1.0G4.0 configuration has a g0 of 5.8 cm-1 (point C) and a small dg/dJ of 0.75×10-3 cm/A. The A0.5G4.0P1.0 configuration has a near saturated g0 of 5.85 cm-1 (point D) and the smallest dg/dJ of 0.6×10-3 cm/A.

The pulse width (left) and the peak power (right) of the different multi-section QD MLL configurations compared with the A0.5G5.0 configuration. (a) A0.5P0.5G4.5 and A0.5P1.0G4.0 configurations. (b) A0.5G4.5P0.5 and A0.5G4.0P1.0 configurations. (c) A0.5G3.0G2.0 configuration.

Stabilty maps of the optical pulse width (left) and peak power (right) vs. gain current and absorber voltage for the GAG configurations. (a) The fundamental harmonic mode-locking. Section 11 was reverse biased as the absorber. (b) The 2nd harmonic mode-locking. The section 6 was reverse biased as the absorber. (c) The 3nd harmonic mode-locking. The section 8 was reverse biased as the absorber. An extra-broad operation range with pulse width below 10 ps was obtained due to symmetric pulse collision.

(a). The pulse shape of the G3.0A0.5G2.0 configuration with a gain current density of 857 A/cm2 and a reverse bias of 1V. The absorber is positioned at site 5, corresponding to 7th harmonic mode locking. The pulse width is 6 ps and the peak pulsed power is 70 mW. (b) The pulse shape of the incomplete mode-locking at 115 GHz with the absorber at section 9 and biased at 0 V. The gain current is 120 mA.